In recent years, a radio wave communication system has become available along with portable terminals. Recently, shorter wavelength infrared rays have been widely used due to available frequency depletion. Other than available frequency depletion, radio waves may influence medical devices or various precision equipment. Moreover, there is fear that infrared rays may adversely influence the human body (e.g., eyes). As a result, optical communication is in the spotlight as a safe communication method.
Meanwhile, white LEDs are developed owing to the success of development of blue LEDs. The features of white LEDs are: extremely lower power consumption than that of conventional incandescent lamps or fluorescent lamps, small size, and long life. Accordingly, use of white LEDs as a illuminative light source is considered. Another feature of white LEDs is a fast response speed relative to supplied power. Paying attention to these features, a study of electrically controlling blinking or light intensity and thereby transferring a signal has been conducted.
A study of integration of such signal transfer using white LED lights with the aforementioned power-line communication system has been conducted. For example, a proposal regarding that study has been disclosed in ‘INTEGRATED SYSTEM OF WHITE LED VISIBLE-LIGHT COMMUNICATION AND POWER-LINE COMMUNICATION’ written by inventors: T. Komine, Y Tanaka, and M. Nakagawa, Institute of Electronics, Information, and Communication Engineers Technical Research Report, The Institute of Electronics, Information, and Communication Engineers, Mar. 12, 2002, Vol. 101, No. 726, pp. 99-104. Since such system utilizes lights, there are no effects on the human body, allowing safe communication. In addition, other applications are expected.